1. Field
This disclosure relates generally to apparatus and methods for use with spinal surgery and, more particularly, to apparatus and methods for precise spinal surgery disc placement.
2. Background
Chronic lower back pain caused by degenerative disc disease is one of the leading causes of disability in adults. Intervertebral disc degeneration can occur as part of the normal aging process in which the nucleus of the disc dehydrates, reducing the shock absorbing capability of the disc. Patients who fail to obtain adequate pain relief from non-surgical treatment (e.g., rest, pain medication, physical therapy, exercise, epidural steroid injections, chiropractic manipulation, ultrasound, massage, orthotics, etc.) may require spinal surgery to alleviate discogenic pain and disability.
One method of treating degenerative disc disease is spinal fusion or arthrodesis surgery in which the affected vertebrae are fused together using a bone graft. Another approach for treating degenerative disc disease is total disc replacement (“TDR”) in which the pain-generating intervertebral disc is removed and a metallic artificial disc implant that allows motion is inserted into the intervertebral space between the adjacent vertebrae. The implanted spinal fusion cage or TDR implant (collectively referred to as “intervertebral implant”) must be appropriately sized to restore the normal disc height at the affected vertebral segment, thereby reducing chronic discogenic pain, while maintaining or minimizing loss of range of motion in the affected vertebral segment.
It is estimated that approximately 3% of fusions and 3-8% of TDR procedures performed each year require revision. Some of these revisions are believed to be due to the misplacement and incorrect size selection of the intervertebral implant (e.g., artificial disc or fusion cage), which is based predominantly on the judgment of the surgeon at the time of the procedure.
Currently, there exist a variety of devices and methods for use in spinal surgery that are related to spinal disc space distractors. For instance, FIG. 1 shows a spinal disc space distractor that is depicted in U.S. Pat. No. 6,261,296 (“the '296 patent”). Devices such as those disclosed in the '296 patent provide grip and tightening mechanisms that are useful due to their mechanical advantages. Although the distractor device disclosed in the '296 patent is capable of opening up the disc (intervertebral) space, such conventional distractor devices do not provide the surgeon with the ability to accurately measure endplate length and disc height for the optimal selection, sizing and placement of the artificial disc, fusion cage or other intervertebral implant. Instead, the selection, sizing and placement of the artificial disc or fusion cage are based predominantly on the judgment of the surgeon at the time of the procedure.
Because conventional distractors lack measuring capabilities, discs may be distracted too much or too little, or the intervertebral implant may be placed in the wrong position. Incorrect selection, sizing and placement of the artificial disc or fusion cage may lead to many serious post-operative complications.
For instance, if the implant selected is too large for the intervertebral space, the implant could over-stuff the intervertebral space, which can reduce the patient's range of motion. Furthermore, if the surgery is a total disc replacement and the implant selected is too large for the space, the implant could create a fusion, instead of preserving the patient's range of motion. If the implant selected is too small, the implant could slip out when the disc annulus is relaxed and nick an artery or the spinal cord, resulting in paralysis or death.
Improper placement of the implant can also lead to improper stress on the surrounding intervertebral bodies, which often necessitates more surgery. Placement of the implant too far anterior may cause the spine to have reduced flexion and enhanced extension. Placement of the implant too far posterior may cause the spine to have enhanced flexion and reduced extension of the spine. Both of the aforementioned scenarios are abnormal for the function of the spine and could also lead to improper loading and stressing of the entire spine.
Conventional spinal distractor devices do not provide the surgeon with the ability to accurately measure the intervertebral disc space to facilitate the proper selection, sizing and placement of the intervertebral implant (e.g., artificial disc or fusion cage).